The present invention relates generally to the field of liquid filtration and specifically to the field of milk filtration.
In normal dairy processing on a farm milk is filtered by pumping the liquid through tubing containing a filter assembly consisting of a filter sock, a rigid support which keeps the filter sock from collapsing upon itself and a retainer which holds the assembly together and allows it to be attached to the tubing at a junction where two pieces of tubing are joined together.
The typical milk filter assembly (FIG. 2, prior art) is constructed by combining a rubber retainer, a support such as coil, and a filter sock so that they can be inserted into a milk tube and clamped in place. The support coil has two ends and looks like a typical Helical compression spring coil. The filter sock is a tube of filter material having one open end and one closed end. The assembly is made as follows: One end of the support coil is placed inside the inside diameter of the rubber retainer while the other end remains free. The filter sock is then passed over the free end, up the coil, and over the outside of the retainer until it reaches the lip of the retainer. The typical filter sock used in this case does not fit snugly around the circumference of the support and is longer than the frame by about two inches. The filter sock must be wide enough to fit over the retainer which is larger in diameter than the coil. This creates an excess of unsupported filter material around the coil. Next, this excess filter material is rolled around the coil to facilitate placement of the coil in the milk tube. The assembly is now placed inside the milk tube. The open end of the filter sock is secured to the outside surface of the retainer by a friction fit between the inside diameter of the tubing and the outside diameter of the sock supported by the outside diameter of the retainer. This holds the sock in place on the retainer with the support coil inside the sock. The fit of the retainer within the wall of the milk tube is determined by the use of a ferrule surrounding the tubing. How good the fit is depends upon how the ferrule is installed. An expansion tool is normally used to do this; the diameter of expansion and thus fit is determined by the pressure exerted by the user of the expansion tool.
Alternatively, the support may be a circular metal frame with a lip on the one end and a protective metal cap on the other end. (FIG. 8, prior art). Large rectangular open areas allow liquid passage. The filter sock is passed over the cap end up to the lip where it is secured by an O-ring which is essentially a rubber band. Again, the typical filter sock used in this case does not fit snugly around the circumference of the support and is longer than the frame by about an inch. This excess of material allows the pressure of the milk, as it is pumped through the filter media, to push the loose media into open areas where it chafes against the edges of the open areas. The milk pressure alternates on and off in cycles which aggravates this chafing action causing rupture of the media. This structure is typical of the SURGE milk filter assembly sold by the Babson Brothers Company of Oak Ridge, Ill.
Additionally, now referring to FIG. 7, another known type of prior art filter assembly is the DeLaval assembly which is sold by the DeLaval company of Kansas City, Mo. The DeLaval structure has a ferrule that screws onto the coil. The ferrule has a lip for attachment to the tubing at a tubing joint. The other end of the ferrule has a small tooth-like projection that acts as a male thread to allow the to be screwed onto the coil. The coil has a uniform wide pitch except for two to three turns at each end which are more closely pitched. The turns at the first end to act as female threads to allow the ferrule to be screwed on. The turns at the other end are designed to turn the end of the coil so it does not puncture the filter sock. The filter sock is passed over the end of the coil up to the lip of the ferrule where it is secured by an O-ring. The DeLaval coil is subject to objectional compression due to the pressure of the milk flow which allows the excess filter material to insert itself between the coils where it is subject to chafing and breakage. The chafing is aggravated by the sharp edges of the metal ferrule at the attachment point of the ferrule and the coil, as well as the edge of the tooth-like projection.
More importantly, the turns of the coil of the DeLaval structure are quite different from the present invention. In the DeLaval structure the first two turns of the coil are quite close together with the remainder of the turns quite far apart. The consequence of this is that the support structure of DeLaval has a tendency to compress and this compression is undesirable because it can lead to binding and chafing of the filter media. The structure of the present invention avoids this by presenting a filter assembly design having maximum rigidity of support structure and availability of filter surface area.
These types of assemblies, while adequate, suffer from several drawbacks.
First, the diameter of the filter sock or media must be sized to the outer circumference of the retainer to achieve a seal against the inside diameter of the tubing, through which the milk is pumped and to which the filter assembly is attached. However, because the diameter of the support coil is much less than the outside diameter of the retainer there is an excess of unsupported filter media collapsing around the support coil whereby the filter media folds in upon itself forming areas of multiple layers of filter media. This leaves 18 to 20% of the surface area of the filter sock unavailable for effective filtering.
Second, because the filter supports in the field are of varying lengths the filter sock is necessarily longer than the support coil and consequently the support coil does not extend all the way down to the bottom of the filter sock. This leaves about one inch of unsupported filter media which then either folds over the outside of the coil or bunches up around the circumference of the coil. This excess material is available to work its way into the open areas of the coil or support and subject the media to breakage due to chafing.
Third, because the width of the sock is dictated by the necessity of fitting it over the outside of the retainer, the cost of the filter sock is increased and it is impossible to achieve a smooth fit over the support coil.
Fourth, the internal support structure or coil is designed such that it does not take into account the fact that the pressure of the milk on the filter sock or media is not uniform as the milk is pumped through. The pressure increases as the milk flows out toward the opening in the retainer. This is because the opening is narrower in diameter than the tube itself. Because of this it is possible for excess unsupported material to be forced in between gaps in the filter support coil. This causes the filter material to be worked against the surface of the support coil and the rubber retainer such that the filter sock can break causing sediment to be deposited in the milk which decreases the value of the milk.
Fifth, in addition to the above it is known that the filter material from which the filter sock is made swells when exposed to a liquid. This causes a good seal to be formed between the filter material and the pipe but results in making it difficult to easily remove the filter assembly after the milk has been filtered. Typically, a pliers or some other tool must be used to grab on to the filter assembly so that it can be freed from the tube.
The present invention, by means of a unique design, overcomes these problems and provides a stable and longer lasting filter system for the milk fluid. The inventor knows of no prior art which discloses the unique features of the present invention.